diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java
index afc6b762222..244e9466ded 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java
@@ -4095,6 +4095,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut2.kt");
             }
 
+            @Test
+            @TestMetadata("IsErasedAllowFromOut3.kt")
+            public void testIsErasedAllowFromOut3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt");
+            }
+
             @Test
             @TestMetadata("IsErasedAllowFromOutAtClass.kt")
             public void testIsErasedAllowFromOutAtClass() throws Exception {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java
index b8510243966..8ee1d405e82 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java
@@ -4095,6 +4095,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut2.kt");
             }
 
+            @Test
+            @TestMetadata("IsErasedAllowFromOut3.kt")
+            public void testIsErasedAllowFromOut3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt");
+            }
+
             @Test
             @TestMetadata("IsErasedAllowFromOutAtClass.kt")
             public void testIsErasedAllowFromOutAtClass() throws Exception {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java
index 7d292ba95cb..82ea5420cc2 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java
@@ -4095,6 +4095,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut2.kt");
             }
 
+            @Test
+            @TestMetadata("IsErasedAllowFromOut3.kt")
+            public void testIsErasedAllowFromOut3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt");
+            }
+
             @Test
             @TestMetadata("IsErasedAllowFromOutAtClass.kt")
             public void testIsErasedAllowFromOutAtClass() throws Exception {
diff --git a/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt b/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt
index 0ee0bd79ec7..3094fea933f 100644
--- a/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt
+++ b/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt
@@ -1102,7 +1102,7 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
     }
 
     val CASTS_AND_IS_CHECKS by object : DiagnosticGroup("Casts and is-checks") {
-        val CANNOT_CHECK_FOR_ERASED by warning<PsiElement> {
+        val CANNOT_CHECK_FOR_ERASED by error<PsiElement> {
             parameter<ConeKotlinType>("type")
         }
         val CAST_NEVER_SUCCEEDS by warning<KtBinaryExpressionWithTypeRHS>(PositioningStrategy.OPERATOR)
diff --git a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
index fd68629e4cc..2c427713a23 100644
--- a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
+++ b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
@@ -590,7 +590,7 @@ object FirErrors {
     val USELESS_ELVIS_RIGHT_IS_NULL by warning0<KtBinaryExpression>(SourceElementPositioningStrategies.USELESS_ELVIS)
 
     // Casts and is-checks
-    val CANNOT_CHECK_FOR_ERASED by warning1<PsiElement, ConeKotlinType>()
+    val CANNOT_CHECK_FOR_ERASED by error1<PsiElement, ConeKotlinType>()
     val CAST_NEVER_SUCCEEDS by warning0<KtBinaryExpressionWithTypeRHS>(SourceElementPositioningStrategies.OPERATOR)
     val USELESS_CAST by warning0<KtBinaryExpressionWithTypeRHS>(SourceElementPositioningStrategies.AS_TYPE)
     val UNCHECKED_CAST by warning2<KtBinaryExpressionWithTypeRHS, ConeKotlinType, ConeKotlinType>(SourceElementPositioningStrategies.AS_TYPE)
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirCastDiagnosticsHelpers.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirCastDiagnosticsHelpers.kt
index b45b46fcbe8..ed4bb56fee2 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirCastDiagnosticsHelpers.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirCastDiagnosticsHelpers.kt
@@ -237,17 +237,12 @@ fun findStaticallyKnownSubtype(
         // If some parameters are not determined by unification, it means that these parameters are lost,
         // let's put ConeStubType instead, so that we can only cast to something like List<*>, e.g. (a: Any) as List<*>
         for (variable in variables) {
-            val value = substitution[variable]
-            val resultValue = if (value == null) {
-                if (!resultSubstitution.containsKey(variable)) {
-                    context.session.builtinTypes.nullableAnyType.type
-                } else {
-                    null
+            val resultValue = when (val value = substitution[variable]) {
+                null -> null
+                is ConeStarProjection -> {
+                    ConeStubTypeForTypeVariableInSubtyping(ConeTypeVariable("", null), ConeNullability.NULLABLE)
                 }
-            } else if (value is ConeStarProjection) {
-                ConeStubTypeForTypeVariableInSubtyping(ConeTypeVariable("", variable.toLookupTag()), ConeNullability.NULLABLE)
-            } else {
-                value.type
+                else -> value.type
             }
             if (resultValue != null) {
                 resultSubstitution[variable] = resultValue
diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt
index 6321e4017a4..2733a5dde33 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt
@@ -606,7 +606,8 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
 
     private fun FirTypeRef.withTypeArgumentsForBareType(argument: FirExpression, operation: FirOperation): FirTypeRef {
         val type = coneTypeSafe<ConeClassLikeType>() ?: return this
-        if (type.typeArguments.isNotEmpty()) return this
+        if (type.typeArguments.isNotEmpty()) return this // TODO: Incorrect for local classes.
+        // TODO: Check equality of size of arguments and parameters?
 
         val firClass = type.lookupTag.toSymbol(session)?.fir ?: return this
         if (firClass.typeParameters.isEmpty()) return this
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt b/compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt
new file mode 100644
index 00000000000..32ec75604f3
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt
@@ -0,0 +1,4 @@
+// FIR_IDENTICAL
+open class Base
+class Derived<E : CharSequence> : Base()
+fun f(entry: Base) = entry is Derived<out CharSequence>
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.txt b/compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.txt
new file mode 100644
index 00000000000..548a826565a
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.txt
@@ -0,0 +1,17 @@
+package
+
+public fun f(/*0*/ entry: Base): kotlin.Boolean
+
+public open class Base {
+    public constructor Base()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Derived</*0*/ E : kotlin.CharSequence> : Base {
+    public constructor Derived</*0*/ E : kotlin.CharSequence>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
diff --git a/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.fir.kt b/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.fir.kt
index 6d7618c501e..6b2ad475fd3 100644
--- a/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.fir.kt
+++ b/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.fir.kt
@@ -6,11 +6,11 @@ fun <E> foo(x: Any, y: Any) : Any {
     }
 
     if (1 == 2) {
-        x <!UNCHECKED_CAST!>as C<!>
+        x as C
     }
 
     if (2 == 3) {
-        x <!UNCHECKED_CAST!>as? C<!>
+        x as? C
     }
 
     class Outer<F> {
@@ -22,7 +22,12 @@ fun <E> foo(x: Any, y: Any) : Any {
         return y
     }
 
-    y <!UNCHECKED_CAST!>as Outer<*>.Inner<!>
+    if (y is Outer<*>.Inner) {
+        return y
+    }
+
+    y as Outer<*>.Inner
+    y as Outer.Inner
 
     return C()
 }
diff --git a/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.kt b/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.kt
index ecdcb99eb61..102c56b2db3 100644
--- a/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.kt
+++ b/compiler/testData/diagnostics/tests/generics/capturedParameters/uncheckedCast.kt
@@ -22,7 +22,12 @@ fun <E> foo(x: Any, y: Any) : Any {
         return y
     }
 
+    if (y is <!CANNOT_CHECK_FOR_ERASED!>Outer<*>.Inner<!>) {
+        return y
+    }
+
     y <!UNCHECKED_CAST!>as Outer<*>.Inner<!>
+    y <!USELESS_CAST!>as <!NO_TYPE_ARGUMENTS_ON_RHS!>Outer.Inner<!><!>
 
     return C()
 }
diff --git a/compiler/testData/diagnostics/tests/smartCasts/kt10444.fir.kt b/compiler/testData/diagnostics/tests/smartCasts/kt10444.fir.kt
index 2f96dbc0e95..8c753c72aed 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/kt10444.fir.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/kt10444.fir.kt
@@ -4,7 +4,7 @@
 class Base<in T>
 class Qwe<T : Any>(val a: T?) {
     fun test1(obj: Any) {
-        obj <!UNCHECKED_CAST!>as Qwe<T><!>
+        obj as Qwe<T>
         check(obj.a)
     }
 
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
index 8979e789739..e9a8e39608a 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
@@ -4101,6 +4101,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut2.kt");
             }
 
+            @Test
+            @TestMetadata("IsErasedAllowFromOut3.kt")
+            public void testIsErasedAllowFromOut3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/IsErasedAllowFromOut3.kt");
+            }
+
             @Test
             @TestMetadata("IsErasedAllowFromOutAtClass.kt")
             public void testIsErasedAllowFromOutAtClass() throws Exception {